In general, devises for air brake operations include a threaded portion for connecting to an air brake system, for example for a motor vehicle. For example, the clevis is attached to an air cylinder by means of threaded rod engaged with a threaded opening in the base of the U-shaped clevis. The rod is adjustable on the road to enable the clevis to be positioned for proper function of the automatic brake adjuster mechanism. Operation of the vehicle places large stresses and destructive loads on the clevis. For example, a typical air chamber associated with an air brake system has an area of 30 sq. in. and is operated at air pressures up to 120 psi. This produces forces of approximately 3,600 lbs force on the clevis threaded joint. Engineering tests and field testing have demonstrated that a clevis must have a minimum of 0.500 inch of thread engagement with the rod to provide adequate threaded joint integrity under the duty cycles noted above. If the threaded attachment between the air chamber rod and the clevis fails, the braking ability of the vehicle is reduced.
It is known to fabricate a clevis with a simple U-shape for an air brake application by casting. However, casting is a relatively slow and expensive operation. For example, a mold must be formed, the actual casting and cooling requires a relatively long time span, and finishing operations are needed to remove imperfections inherent in the casting process. In addition, the casting process inherently produces unusable product, further increasing cost and time. Further, casting operations have undesirable environmental impacts associated with high energy usage, air and water emissions, and disposal of hazardous materials used in the molding and casting operations. Finally, casting constraints limit shapes, for example, more complicated internal configurations, that can be produced by casting operations.
It is known to fabricate a clevis by stamping steel approximately 0.24-0.25 inches thick. The stamped clevis has had the same simple “U” shape as the cast clevis with a threaded opening in the base of the “U” shape. However, when the threaded rod is engaged with the threaded opening in the base of the “U”, the prior art stamped clevis design results in only 0.24-0.25 inches of thread engagement (the thickness of the piece from which the clevis is stamped and through which the threaded opening passes). This thread engagement length does not provide proper joint integrity and as a result a known clevis stamped from steel approximately 0.24-0.25 inches thick is not acceptable for use due to unacceptable joint durability.
It is known to fabricate a clevis by stamping steel approximately 0.24-0.25 inches thick with the same simple “U” shape as the cast clevis and having a smooth opening in the base of the “U” shape. In this case, the rod extending out of the air chamber passes through the opening and is welded to the clevis to provide the required joint strength for the clevis to rod interface. However, the welded joint precludes any adjustment of the rod with respect to the clevis and increases the cost and complexity of the clevis and air system interface.